1. Field of the Invention
This invention relates generally to a magnetic recording apparatus and, more particularly, is directed to a rotary disc of a magnetic recording apparatus on which an information record disc is mounted.
2. Description of the Prior Art
An information record disc has previously been used for recording video information signals in magnetic recording apparatus, such as a video camera, in a plurality, for example, twenty-five, spiral tracks thereon, with one field of video signals being recorded in each track and one field of a still-picture being reproduced by scanning each track. Generally, the information record disc includes a central core and a yoke made of a magnetic material secured at the underside of the central core, the yoke including a projection which extends to a position at the upper surface of the central core.
The magnetic recording apparatus includes a rotary disc mounted on a rotatable shaft and which supports and positions the information record disc in the apparatus. More particularly, the rotary disc includes an outwardly extending radial flange on which an annular magnet is positioned for magnetically attracting the information record disc and, more particularly, the yoke thereof. An annular support member is also positioned on the outwardly extending radial flange of the rotary disc in surrounding relation to the magnet. The support member is also made of a magnetic material and extends to a height above the magnet so as to provide a circular support surface upon which the information record disc and, more particularly, the yoke thereof, rests. At such time, the yoke is held firmly with the annular support member by magnetic attraction from the magnet so as to securely position the information record disc in the magnetic recording apparatus. In addition, a magnetic flux detector of the magnetic recording apparatus is provided which is positioned once during each revolution of the information record disc in opposing relation to the projecton of the yoke which extends to the upper surface of the information record disc, for example, for determining the speed and/or phase of rotation of the information record disc.
However, with the magnetic recording apparatus according to the prior art, because the information record disc is supported on the annular support member at a higher position than the magnet of the magnetic recording apparatus, a high output magnetic flux at the projection of the yoke at the upper surface of the information record disc is difficult to obtain. Accordingly, only a small leakage flux is obtained thereat for detection by the magnetic flux detector. Another problem with the magnetic recording apparatus according to the prior art is that the contact between the yoke and the upper surface of the annular support member may not be flush. In other words, because both contact surfaces thereof are circular, any irregularities or deformaties in the flatness of the surfaces will cause poor contact therebetween. In addition, magnetic powder or the like may be attracted on the upper surface of the annular support member, thereby resulting in further irregularities in the surfaces so as to further decrease the stability of contact between the two surfaces.